Pipe mill

ABSTRACT

A pipe or tube mill of the cage-type having improvements in the breakdown, preforming and edge forming of the strip reducing the cost of tooling and enhancing the convertibility of the mill to produce tubes or pipe of different sizes and yet which can readily handle heavy gauge strip.

nited States Patent @hang 5] Jan. 18, 1972 [54] PIPE MILL 3,472,053 10/1969 Chang ..72/ 178 2,164,836 7/1939 Penkala.... [72] Invent will! Chang Rcky ohm 3,462,989 8/1969 Fischer, Jr. ..72/181 x [73] Assignee: The Yoder Company, Cleveland, Ohio 3,417,591 12/1968 Babbitt ..72/181 3 370,448 2/1968 Ruple.....

l l9 [22] ed 69 3,323,341 6/1967 Chang ..72/176 [21] Appl. No.: 875,251

Primary Examiner-Milton S. Mehr 52 0.5. cu. ..72/178, 72/181 MOW-Oberlin Maky, & 51] 1111. (:1 ..nzm s/os' [58] Field Search ..72/181, 178, 179, 182, 176 ABSTRACT I A pipe or tube mill of the cage-type having improvements in [56] References Cited the breakdown, preforming and edge forming of the strip UNITED STATES PATENTS reducing the cost of tooling and enhancing the convertibility of the mill to produce tubesor pipe of different sizes and yet 2,01 Park 81 can readily handle gauge 1,822,984 9/1931 Watkins.. .....72/18l 3,468,150 9/1969 Ruple ..72/ 178 13 Claims, 11 Drawing Figures PATENTEU JAM 8 m2 SHEET U U? 5 INVENTOR WILL/AM J. H. CHANG mcmsodmsmz I 3.635.064 SHEET 5 [1F 5 mvmon w/LL/AM J. H. CHANG fi zhuizw pmdl gm ATTORNEYS PIPE MILL This invention relates generally as indicated to a pipe mill and more particularly to certain improvements in a tube or pipe mill of the type disclosed in applicants US. Pat. Nos. 3,323,341 and 3,472,053.

In such mills, breakdown passes comprising extremely large power-driven rolls are required for shaping and driving the strip through the mill. For larger pipe sizes several such breakdowns may be required. Such breakdowns and particularly the tooling therein add to the cost of the mill and make it difficult to convert the mill from one size to another. Also, it is difficult to get the strip into breakdowns and this is particularly a problem with thicker or heavier gauge strip.

It is accordingly a principal object of the present invention to provide a pipe or tube mill having a strip preformer which will aid in getting the strip into the initial breakdown or which may eliminate the need for a breakdown.

Another important object is the provision of such mill having an entry table which incorporates the preformer greatly facilitating the threading of the strip into the mill.

Yet another object is the provision of a preformer which can be adjusted to accommodate strip of different size without expensive and time-consuming tooling changes.

Still another object is the provision of improved edge forming using edge-forming units having readily changeable tooling.

A further object relates the provision of an edge-forming unit wherein each set of rolls is mounted on a quickly adjustable or removable plate, each roll being joumaled in cantilever fashion.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

In said annexed drawings:

FIG. I is a side elevation partially broken away of a mill in accordance with the present invention;

FIG. 2 is a top plan view of the mill seen in FIG. 1;

FIG. 3 is an enlarged vertical elevation of the support for the edge-forming device as seen from the line 33 in FIG. I, each edge-forming roll subassembly being shown in phantom lines;

FIG. 4 is an enlarged horizontal section taken substantially on the line 44 of FIG. 3;

FIG. 5 is an enlarged fragmentary detail view partially in section showing the cantilever mounting of the rolls of one of the edge-forming roll subassemblies;

FIG. 6 is a fragmentary section taken substantially on the line 66 of FIG. 5;

FIG. 7 is an elevation of the rolls seen from the line 7-7 of FIG. 5;

FIG. 8 is a fragmentary enlarged side elevation of the preforming unit;

FIG. 9 is an end elevation of such preforming unit as seen substantially from the line 99 of FIG. 8;

FIG. 10 is an illustration of the successive inclination of one of each pair of the bottom rolls of the preforming unit; and

FIG. 11 is a fragmentary end elevation partially in section of an alternative form of edge forming device which may form the edges of the strip while still fiat.

Referring first to FIGS. 1 and 2, it will be seen that the strip enters from the left in both views from entry conveyor 10 and moves onto the table of slightly downwardly inclined preformer conveyor 11. Such preformer conveyor centers or aligns the strip with the centerline of the mill and conditions it with a preformer unit on the exit end thereof to pass into the initial breakdown shown generally at 12. From the initial breakdown, the strip passes into a cage roll assembly 13 which will substantially form the strip into circular shape. From the cage roll assembly, the strip then passes into the initial fin pass shown generally at 14. From the tin passes, the strip passes into the welder and emerges as pipe or tubing and is severed into lengths for further processing.

From the entry conveyor 10, the strip passes over shelf I6, idler roll 17, shelf 18 and into the nip of pinch roll unit 19 which is driven by motor 20 through reducer 21. The shelves, idler roll and pinch roll unit are mounted at the entry end of the preformer conveyor 11. The strip then passes through edge guide units 23 and 24 separated by idler 25. The edge guide units may be adjusted through handwheels seen at 26 to accommodate strip of different widths and in any event to precisely align the strip with the centerline of the mill.

From the edge guide device 24, the strip passes into preforming unit 28 at the exit end of the preforming conveyor 11. The preforming unit is shown in greater detail in FIGS. 8, 9 and 10. Such preforming unit dishes the strip slightly beyond its yield point and enables the strip to move easily into the first breakdown 12.

The first breakdown may be generally conventional and both the top and bottom rolls are driven by large drive motor 30 through reducer 31. The top roll is seen at 32 and the bottom roll has a mating female configuration. The top roll may be moved vertically by adjustment of handwheel 33.

Mounted on the exit side of the first breakdown 12 is an edge-forming device 34 operative to bend the lateral edges of the strip on a radius shorter than that of the main portion of the strip. This facilitates the final shaping of the strip into the circular tubular or pipe form. The edge-forming device 34 is shown in greater detail in FIGS. 3 through 7.

The strip now passes into the cage roll assembly 13 which comprises a plurality of idler rolls 36 mounted on beams 37 which are in turn each mounted on a pair of inclined stands 38 and 39 so that the beams may be adjustably positioned along such stands at each end. The stands extend transversely of the mill centerline and are symmetrically disposed. In the illustrated embodiment there are three beams and two stands for each beam on each side of the mill. In this manner, the idler rolls 36 substantially follow the same longitudinal position on the strip as the strip is formed from the relatively shallow dish shape leaving the edge forming device to a substantially circular shape entering the fin passes 14.

Overhead bridge frames 41 and 42 support therebetween longitudinally extending frame 43. The frame 43 supports for vertical movement hold-down rolls 45 and 46 through adjustments indicated at 47 and 48, respectively, such hold-down rolls forcing the strip against bottom driven rolls, not shown, driven from shafts 49 and 50 through transmission 51 from reducer 52 driven by drive motor 53.

The longitudinal top frame 43 also supports for vertical adjustment interior side roll cluster assemblies 54 and 55. For a more detailed disclosure of the cage roll assemblies reference may be had to the more recent of applicants above-noted US. patents.

From the cage roll assemblies, the now substantially circularized strip passes into the initial fin pass 14, each roll of which may be power driven through drive motors 58 and reducers 59. The top roll of each pass may be vertically moved by adjustment of handwheel 60.

Referring now additionally to FIGS. 3 and 4, it will be seen that the edge-forming device 34 is mounted on the base 70 of the initial breakdown 12, such base in turn being mounted on longitudinally extending rails 71 and 72. The edge-forming device includes a fabricated subbase 73 supporting jacks 74 and 75, both of which may be operated in unison through line shaft 76. The jacks 74 and- 75 support base 77 which in turn supports vertically extending plate 78 on which the edgeforming roll units are mounted. A wrench or other turning tool may be applied to the end 79 of the line shaft 76 to raise and lower the plate 78. A scale and pointer seen at 80 is provided so that the operator may determine the vertical position of the edge forming device.

The plate 78 is provided with a window 82 through which the strip passes. The lateral edges of the plate 78 are slide guided in vertically extending frames 83 and 84 which are connected to the roll housings 85 and 86, respectively, of the initial breakdown and which are interconnected by tie rod 87.

Above the window 82, the plate 78 is provided with vertically aligned apertures seen at 88 and 89 to which edge-forming roll units, seen in phantom lines in FIG. 3, may be coaxially pivotally connected. The top of the plate 78 is also provided with symmetrically positioned apertures 90 accommodating pivot pins 91 on which are mounted yokes 92. As seen at 93, the plate 78 is provided with strategically arranged tapped apertures adapted to accommodate clamping bolts firmly to hold the edge-forming roll units in proper adjusted position. At each lower corner of the plate 78 there is provided arcuate clamping plates 94, each being provided with three-clamping fasteners 95.

Referring now to FIGS. 5, 6 and 7, it will be seen that the edge-forming device includes a rightand left-hand edgeforming unit indicated at 97 and 98, the left-hand unit being broken away but substantially the mirror image of the righthand unit. Each roll unit includes a baseplate 99 on which is secured roll housing 100. The housing 100 is provided with blocks 101 and 102 in which roll shaft 103 is joumaled by the axially spaced tapered roller bearings seen at 104 and 105;

Female edge-forming roll 106 projects from the housing in the cantilevered fashion indicated.

The male edge-forming roll 107 is mounted on roll shaft 108 similarly journaled at 109 and 110 in blocks 112 and 113. The blocks 112 and 113 are interconnected by a sleeve 114 and such latter blocks are mounted in windows 115 and 116 at each side of the housing. The lateral edges of the windows form guides for movement of the male roll 107, such movement being obtained by jackscrews 118 and 119 which extend through oppositely flanged thrust nuts 120 and 121, respectively, secured in end wall 122 on the housing 100. Such jackscrews extend through thrust bushings in plate 123, such plate bridging and being secured to the blocks 112 and 113 by the fasteners indicated in FIG. 7. Each jackscrew is provided with a pinion on its inner end as seen at 124 and 125, such pinions meshing with intermediate idler 126. In this manner rotation of either of the jackscrews will obtain uniform movement of the male roll 107 toward and away from the female roll 106. The roll construction of unit 98 may be the same.

The plate 99 is provided with an offset tab 128 having aperture 129. The plate of the roll unit 98 is provided with a tab in its own plane as seen at 130. In this manner, the plates are adapted to be coaxially pivotally connected to bushing 131 mounted in aperture 89 of the plate 78 seen in FIG. 4. Such bushing is held in place by fastener 132 threadedly connected to plate 133 secured to the back of plate 78 by fasteners 134.

The top of each plate is provided with a .l-shape stiffening flange seen at 136 secured at one end to the housing 100. The opposite end passes adjacent aperture 137 in plate 99 and a plate 138 is secured to the outer end of the stiffening flange, such plate 138 being parallel to the plate 99 and provided with aperture 139 aligned with the aperture 137.

The plate of the roll unit 98 is provided with a similar aperture and flange construction at its upper corner as indicated at 140. As seen in FIGS. 3 and 4, each such aperture construction is provided with a pin 142. The pin is retained in place by a keeper 143 secured to the outer plate. Between the plates the pin fits through hub 144 which has projecting therefrom threaded stud 145. Such threaded studs are thus pivotally connected to the upper ends of each plate and extend through aligned apertures in the legs of the yokes 92 and through a nut supported between thrust washers 146, such nut being turned by reversible ratchet handles 147. By operation of the ratchet handles, the position of the edge forming'units on the plate 78 may be adjusted about their coaxial center pivot seen at in FIG. 5.

Each of the roll mounting plates is provided with a pair of slots extending generally circumferentially of the pivot as indicated at 151 and 152 and large clamping fasteners 153 and 154 are employed in association with the tapped apertures 93 in the plate 78 to assist in locking the roll-supporting plates 99 in the selected position. The lower arcuate edge of the plates 99 is provided with a shelf seen at 155 which fits underneath the arcuate edges of the bottom clamps 94. When the clamps and the fasteners are loosened, the ratchet handles may be employed to adjust the position of the edge-forming roll units and a pointer on the plates 99 seen at 156 is employed in association with markings 157 on the plate 78 for selected pipe sizes.

For example, the edge-forming unit depicted in FIGS. 5 through 7 may be employed to form pipe of a diameter ranging from 5 9/16 inches to 8% inches. For pipe of larger diameter, different edge-forming units may be secured to the plate 78 and pivoted about the upper pivot aperture 89 seen in FIG. 3 in the same manner that the units of FIG. 5 are pivoted to the lower pivot aperture 88. Thus with two sets of tooling, one set pivoted on a shorter radius and the other set on a longer radius, pipe of a wide variety of sizes may be properly edge formed.

Referring now to FIGS. 8, 9 and 10, in addition to FIG. 1, it will be seen that the preformer conveyor 11 which includes the preforming unit 28 at the exit end thereof is supported at its entry end on jacks 160 and pivotally connected at 161 to the entry conveyor 10. At its exit end it is loosely pivotally connected at 162 to the initial breakdown l2 and supported on jacks 163 at such exit end. The entire preforming conveyor is accordingly adjustably vertically mounted to align the strip S passing therethrough with the initial breakdown pass 12.

The performing unit shown in detail in FIGS. 8, 9 and 10 on the exit end of the preforming conveyor includes two vertical frame members 165 and 166 supporting therebetween top frame 167. The vertical frames 165 and 166 are supported on longitudinal frames 168 and 169 of the preforming conveyor 11 as seen more clearly in FIG. 9. Such longitudinal frames of the conveyor are interconnected by transverse structural members such as those indicated at 171 and 172 in FIG. 8. The structural members of the preforming conveyor support platform plates 173 on which are adjustably mounted subassemblies of lower preforming rolls seen at 174 and 175. In the illustration, each subassembly includes five rolls. Each subas' sembly is directly transversely opposite the other and the rolls of the two subassemblies thus paired are symmetrically disposed with respect to the eenterline of the mill.

As seen more clearly in FIG. 10, each subassembly may include, for example, rolls 178, 179, 180, 181 and 182 inclined respectively with respect to the horizontal at progressively increasing angles. The rollers for each set may have a common work point indicated at 183 with the preforming conveyor in horizontal position. In other words, the upper left-hand corner of each roll looking downstream of the mill is aligned.

Each roll is provided with projecting end shafts seen at 185 and 186 joumaled in pillow blocks 187 and 188, respectively, secured by fasteners 189 to underlying plates 190 of the support frame 191. Each underlying plate 190 for the respective rolls is supported at the angle of inclination of the roll by upwardly stepped frame members 192 and 193 extending Iongitudinally of the mill. Gusset plates 194 are provided between the underlying plates and the bottom plate 195 to provide a rigid support for the five roll set.

Each subframe is secured to a slide plate as seen at 196 and 197 in FIG. 9. Secured to the underside of such slide plates by the fasteners indicated at 198 are gibs 199 guiding and retain ing the slide plates for movement on the platform 173. Journaled for rotation between the side frames 168 and 169 of the preforming conveyor 11 are adjustment screws 201 and 202. Each screw is provided with two threaded portions, one indicated at 203 being 6-pitch left-hand acme threads and the other being 6-pitch right-hand acme threads 204. Each such adjustment screw is provided with a pinion indicated at 205, such pinions being interconnected by drive chain 206 so that rotation of one screw rotates the other. The opposite ends of such screws are provided with squared heads seen at 207 for application of a turning tool.

The threaded portions of each screw are connected to yokes 209 and 210 depending from the slide plates 196 and 197, respectively, so that rotation of the adjustment screws will move the lower roll subassemblies toward and away from the centerline of the mill. For example, the roll assembly 175 can be moved outwardly to the phantom line position seen at 211. As the unit 175 is thus moved outwardly, the unit 174 will be moved outwardly at the same rate to maintain its symmetry with the centerline of the mill. 7

A top roll 212, slightly crowned, is mounted on shaft 213 journaled in legs 214 and 215 of yoke 216 which is mounted for vertical movement in guides 217 and 218. Such vertical movement is obtained by jackscrew 219 secured to the bight portion of the yoke which extends through worm housing 220 on frame 221 positioned above the bridge frame 167. The worm is rotated through line shaft 222 by application of a turning tool to the squared end 223 on the operators side of the mill. The top roll 212 may be power driven through the drive shaft 224 and universal coupling indicated.

The bridge frame 167 includes transversely extending box frame members 225 and 226 as well as relatively short longitudinally extending box frame members 227 and 228 forming a rigid frame for enclosure of the vertical guides for the top roll 212. Relatively short longitudinally extending guide frames 229 and 230 are also secured between the transversely extending box frames 225 and 226 which together with the guide plates 231 and 232 secured to the interior of the transversely extending box frame members confine the yoke supporting the top roll 212 so that it is slide guided for vertical movement on four sides. The yoke includes a scale pointer 233 riding against scale 234, such scale and pointer being visible through window 235 in vertical frame 165.

The yoke also includes an inclined deflector 236 projecting upstream of the mill to assist in guiding the strip into and through the preforming unit.

The lower idler rolls of the preforming unit are thus moved in and out symmetrically to accommodate strip of different width or pipe of different diameter and the top roll is moved up and down accordingly. The top roll may be inserted to varying degrees into the crotch or vertex of the shallow V- formed by the bottom rolls which increase in inclination downstream of the mill. The top roll may be inserted just beyond the yield point of the strip to impart a dish to it.

Not only does the preformer actually form the strip but assists the strip in entering the initial breakdown and from there through the edge-forming rolls into the cage rolls.

More than one top drive roll may be provided in the preformer, andthe bottom idler rolls may be extended to be situated beneath both top rolls. The increased bending performed in this extended preformer can in most cases produce the same total bending obtained in the above-discussed combination of preformer and conventional initial breakdown stand, and result in elimination of a comparatively very expensive breakdown.

The top-crowned rolls 212 may be moved into the crotch of the symmetrically disposed bottom rolls as seen in phantom lines at 240. In this position the strip S may be slightly beyond its yield point and the preformer will actually thus impart a longitudinal bend to the strip.

In the embodiment of the invention seen in FIG. 1, where an initial breakdown is employed, the strip passing through the preformer and into the initial breakdown will have its edges straight as indicated at 241 in FIG. 9. Where the extended preformer is employed in lieu of the initial breakdown the strip may then pass directly through an edge-forming device 34 or preferably the edges of the strip will be formed before passing into the preformer by an edge-forming unit such as seen in FIG. 11.

The unit of FIG. 11 may be incorporated into the prefonning conveyor but in any event the edge forming of the FIG. 11 embodiment is applied to the flat strip S before it enters the prefonner. Such embodiment includes a transversely extending base 243. On one side of the centerline of the mill there is provided a stand 244 having legs 245 and 246 supporting pillow blocks 247 and 248, in which are joumaled the ends of adjustment screw 249. A slide table 250 is threadedly connected to the adjustment screw and is provided with oppositely directed bosses or the like 251 having bushings therein which enclose guide rods 252. The outer end of the screw 249 is pro vided with a squared end 254 permitting the same to be rotated by a turning tool and the inner end is provided with a beveled gear 255 in mesh with bevel gear 256 on the inner end of adjustment screw 257 mounted symmetrically with respect to the adjustment screw 249 on the opposite side of the centerline of the mill. The adjustment screw 257, of course, has opposite hand threads of the same pitch as the screw 249.

' The slide table 2511 supports edge roll unit 259 which may be in substantially all respects the same as the edge roll units depicted in FIGS. 5, 6 and 7. A top or male roll 260 is moved vertically with respect to the female roll 261 by the adjustments indicated at 262. By application of the turning tool the roll unit may be moved or adjusted to and from the phantom line position seen at 263 to accommodate strip of different widths. If desired, the entire unit may be mounted for vertical adjustment on jacks. By appropriate selection of the angle of inclination 264 of the slide table 251) the edge form device design of FIG. 11 can be applied ahead of, after, or in the center of the extended preformer.

With the combined edge-forming forming unit of FIG. 11 and the power-driven extended preformer of FIG. 9, a universal No. 1 breakdown can be provided. The tooling requirements in such a breakdown considerably reduce the cost of equipment as well as the time of changeover for different diameter pipe. Power may be supplied by a feed pass such as seen at 19 in FIG. 1 or the edge-forming rolls themselves may be power driven.

It will be appreciated that the preformer unit 28 requires no tooling change to accommodate the total mill size range and that the edge-forming unit may have perhaps two or three sets of relatively small rolls to cover the total mill range with such sets being readily applied to and removed from the side tables 250.

It can now be seen that there is provided a pipe or tube mill utilizing for the most part relatively inexpensive tooling which can readily be removed and replaced or adjusted to convert the mill to produce tube or pipe of different diameter. Improved edge forrning is also provided as well as a preforming unit which can be used in lieu of relatively expensive breakdowns properly to shape the strip for entry into the cage roll assembly which converts the strip from the shallow-dished sectional shape seen more clearly in FIG. 9 to the substantially circular shape entering the tin passes.

I, therefore, particularly point out and distinctly claim as my invention:

1. A mill for producing pipe and the like comprising a cage roll assembly, a preforming device ahead of said cage roll assembly, said preforming device comprising a relatively narrow vertically movable top roll, and pairs of symmetrically inclined bottom rolls forming a longitudinally extending shallow generally V-shape trough, the inclination of each succeeding pair increasing, and an edge forming device on the entry side of said preformer operative to impart a radius to the edges of such strip before entry into said preformer.

2. A mill for producing pipe and the like comprising an edge-forming device, said device including a mounting plate having a window therein for passage therethrough of strip to be formed into such pipe, rightand left-hand edge-forming units coaxially pivotally mounted on said plate, each unit including a supporting plate and a housing having a pair of edgeforming rolls projecting inwardly therefrom, and means operative individually to adjust each supporting plate about such coaxial pivot and clamp the same to said mounting plate.

3. A mill as set forth in claim 2 wherein each roll of each pair is mounted on a roll shaft joumaled at axially spaced points in the respective housing.

4. A mill as set forth in claim 3 wherein the top roll of each pair is mounted for movement toward and away from the bottom roll of each pair.

5. A mill as set forth in claim 2 including vertically aligned spaced pivot apertures in said mounting plate operative optionally to support edge-forming units to accommodate strips of different width.

6. A mill as set forth in claim 2 including a cage roll assembly, said edge-forming device being mounted upstream of said cage roll assembly.

7. A mill as set forth in claim 2 wherein each supporting plate includes an arcuate outer edge, the radius of which is struck from such coaxial pivot, and clamp means mounted on said mounting plate operative releasably to engage said arcuate edge.

8. A mill as set forth in claim 2 including slots in said supporting plates extending generally circumferentially of said coaxial pivot, and clamping fasteners extending through said slots and into said mounting plate.

9. A mill as set forth in claim 2 including a threaded stud pivotally connected to the upper end of each supporting plate,

a reversible ratchet nut mounted on each stud, and a yoke for said nut mounted on said mounting plate whereby operation of said reversible ratchet pivots the supporting plate with respect to the mounting plate.

10. A mill as set forth in claim 2 wherein said mounting plate is vertically adjustably mounted on the exit side of a breakdown.

11. A mill as set forth in claim 2 including a preforming device, and a breakdown between said preforming device and said edge forming device.

12. In a pipe mill for converting strip into tubular form, an edge-forming device operative to impart a radius to the edges of such strip passing through said edge-forming device, said edge-forming device including symmetrically transversely adjustable roll sets, each set being movably mounted on an inclined linear path for such adjustment.

13. An edge-forming device as set forth in claim 12 wherein the angle of inclination of said inclined linear path is related to the position of said edge-forming device longitudinally of the mill, said angle increasing downstream of the mill. 

1. A mill for producing pipe and the like comprising a cage roll assembly, a preforming device ahead of said cage roll assembly, said preforming device comprising a relatively narrow vertically movable top roll, and pairs of symmetrically inclined bottom rolls forming a longitudinally extending shallow generally Vshape trough, the inclination of each succeeding pair increasing, and an edge forming device on the entry side of said preformer operative to impart a radius to the edges of such strip before entry into said preformer.
 2. A mill for producing pipe and the like comprising an edge-forming device, said device including a mounting plate having a window therein for passage therethrough of strip to be formed into such pipe, right- and left-hand edge-forming units coaxially pivotally mounted on said plate, each unit including a supporting plate and a housing having a pair of edge-forming rolls projecting inwardly therefrom, and means operative individually to adjust each supporting plate about such coaxial pivot and clamp the same to said mounting plate.
 3. A mill as set forth in claim 2 wherein each roll of each pair is mounted on a roll shaft journaled at axially spaced points in the respective housing.
 4. A mill as set forth in claim 3 wherein the top roll of each pair is mounted for movement toward and away from the bottom roll of each pair.
 5. A mill as set forth in claim 2 including vertically aligned spaced pivot apertures in said mounting plate operative optionally to support edge-forming units to accommodate strips of different width.
 6. A mill as set forth in claim 2 including a cage roll assembly, said edge-forming device being mounted upstream of said cage roll assembly.
 7. A mill as set forth in claim 2 wherein each supporting plate includes an arcuate outer edge, the radius of which is struck from such coaxial pivot, and clamp means mounted on said mounting plate operative releasably to engage said arcuate edge.
 8. A mill as set forth in claim 2 including slots in said supporting plates extending generally circumferentially of said coaxial pivot, and clamping fasteners extending through said slots and into said mounting plate.
 9. A mill as set forth in claim 2 including a threaded stud pivotally connected to the upper end of each supporting plate, a reversible ratchet nut mounted on each stud, and a yoke for said nut mounted on said mounting plate whereby operation of said reversible ratchet pivots the supporting plate with respect to the mounting plate.
 10. A mill as set forth in claim 2 wherein said mounting plate is vertically adjustably mounted on the exit side of a breakdown.
 11. A mill as set forth in claim 2 including a preforming device, and a breakdown between said preforming device and said edge forming device.
 12. In a pipe mill for converting strip into tubular form, an edge-forming device operative to impart a radius to the edges of such strip passing through said edge-forming device, said edge-fOrming device including symmetrically transversely adjustable roll sets, each set being movably mounted on an inclined linear path for such adjustment.
 13. An edge-forming device as set forth in claim 12 wherein the angle of inclination of said inclined linear path is related to the position of said edge-forming device longitudinally of the mill, said angle increasing downstream of the mill. 